1. Field of the Invention
The present invention relates to a device for detecting a leading edge of a recording paper. This device is employed in a printer and a paper magazine using a paper roll of a thermosensitive recording paper, a printing paper and so forth.
2. Description of the Related Art
It is known that some of photographic printers and color thermal printers use a paper roll formed by rolling a strip of a recording paper. The paper roll is contained in a paper supply section of the printer, and is rotated by a driving mechanism so as to be rotated forward in a paper feeding direction and so as to be rotated backward in a rewinding direction. A flange having a rotary shaft is attached to the paper roll. As to ways for supporting the rotary shaft, there are a fixation type and a movement type. In the fixation type, the rotary shaft of the paper roll is rotatably supported at a fixed position. In the movement type, a drive roller abutting on a periphery of the paper roll is provided, and the rotary shaft is moved toward the drive roller in accordance with a diameter change of the paper roll.
Upon rotating the paper roll forward, the recording paper is advanced from the paper supply section to a print section to execute a printing process. After printing, the printed recording paper is cut in a predetermined size and is discharged to the outside of the printer. A region of the recording paper, which has been advanced to the print section but has not been used for printing, is rewound by rotating the paper roll backward. When rewinding the recording paper, there arises a problem in that looseness of winding is caused because the printing paper and the thermosensitive recording paper have a paper thickness and a paper strength.
In order to prevent the looseness of winding, Japanese Patent Laid-Open Publication No. 2000-169013 discloses a method in which the paper roll is rotated backward so as to be securely wound before feeding the paper. After securely winding the paper roll, the recording paper is fed. This method employs a detecting device for a leading edge of the recording paper. This detecting device (hereinafter, leading-edge detecting device) abuts on a peripheral surface of the paper roll to detect the leading edge thereon. Secure winding of the paper roll is judged when a detection interval of the leading-edge detecting device becomes constant during the reverse rotation of the paper roll.
The leading-edge detecting device comprises a basic roller, an actuation lever, a driven roller, and a micro switch. The basic roller abuts on the periphery of the paper roll. The actuation lever rotates around the basic roller. The driven roller is disposed on the actuation lever. When the driven roller overleaps the leading edge of the recording paper, the micro switch outputs a detection signal in response to the movement of the actuation lever.
The actuation lever is urged by a first spring so as to contact the driven roller with the periphery of the paper roll. Meanwhile, the basic roller is supported by a roller supporting lever to which a second spring is attached to contact the basic roller with the periphery of the paper roll. One end of the first spring is attached to the actuation lever, and the other end thereof is attached to the roller supporting lever. The micro switch is disposed at a fixed position in the paper supply section.
However, the above unit for detecting the leading edge has problems in that a number of parts thereof is large and a structure thereof is complicated. Particularly, in the rotary-shaft fixing type, a moving amount of the actuation lever is large in comparison with the rotary-shaft moving type. Thus, there arises another problem in that it is necessary to separately provide a mechanism for moving the micro switch together with the actuation lever.
In view of the foregoing, it is a primary object of the present invention to provide a device for detecting a leading edge of a recording paper, in which the reading edge is detected with a simple structure.
It is a second object of the present invention to provide a device for detecting a leading edge of a recording paper, in which a number of parts thereof is reduced.
In order to achieve the above and other objects, the leading-edge detecting device according to the present invention comprises an abutting member contacting with a periphery of a paper roll, and a vibration detecting sensor for detecting a vibration of the abutting member. The vibration detecting sensor outputs a signal in accordance with a scale of the vibration, and is preferable to be attached to the abutting member.
The paper roll is formed by rolling a strip of a recording paper. While the paper roll is rotated backward in a winding direction, the abutting member overleaps a leading edge of the recording paper every rotation thereof. When the abutting member has overleapt the leading edge, the vibration detecting sensor outputs the signal having a higher level. On the basis of the signal of the higher level, disengagement of the leading edge and the abutting member is judged to detect the leading edge.
In a preferred embodiment, the abutting member is a separator for separating the leading edge from the paper roll. When the paper roll is rotated forward in a paper feeding direction, a head portion of the separator abuts on the lading edge to separate it from the paper roll.
A rotary shaft is set to the paper roll. In a case that the rotary shaft is adapted to be held at a fixed position, it is preferable to provide a drive roller, a first supporting arm, and a first spring. The drive roller abuts on the periphery of the paper roll to rotate it. The first supporting arm moves the drive roller in accordance with a diameter change of the paper roll. The first spring urges the first supporting arm so as to contact the drive roller with the paper roll.
Further, it is preferable to provide a second supporting arm and a second spring. The second supporting arm supports the abutting member. The second spring urges the second supporting arm so as to contact the abutting member with the periphery of the paper roll. The second spring is attached to the first supporting arm so as to move together with the second supporting arm.
According to the present invention, a structure of the leading-edge detecting device may be simplified, and a number of parts thereof may be reduced by utilizing the separator used for separating the leading edge from the periphery of the paper roll. Further, the vibration detecting sensor is attached to the separator so that it is unnecessary to provide a special mechanism for moving the vibration detecting sensor.